Generally, organic light emitting devices can be classified as passive matrix organic light emitting diodes (OLED, organic light emitting diode) and active matrix OLED (AMOLED, active matrix OLED), and according to the manner of driving an EL element, can be classified as current driven OLEDs and voltage driven OLEDs. A typical AMOLED generally includes a plurality of gate lines, a plurality of data lines, a plurality of power lines and a plurality of pixels connected to these lines and arranged in a rectangular form. Each pixel usually includes: one EL element; two transistors, one is a switching transistor used for transmitting a data signal, and the other is a driving transistor used for driving the EL element according to the data signal; and a capacitor used for maintaining the data voltage.
Although the AMOLED has the advantages of low power consumption, however there is a phenomenon that the driving transistor turns on the light emitting diode at a gate potential reset stage, which resulting in insufficient darkness of an OLED display panel when working at a dark state and directly resulting in an insufficient contrast ratio of the OLED display panel.